[PATCH v4 04/15] linux/mm.h: move page_kasan_tag() to mm/page_kasan_tag.h

[Max Kellermann]

Prepare to reduce dependencies on linux/mm.h.

page_kasan_tag() is used by the page_to_virt() macro in ARM64 (but
asm/memory.h does not include linux/mm.h).  Thus, in order to be able to use
anything that calls page_to_virt(), linux/mm.h needs to be included.

This would prevent us from moving page_address() to a separate header,
because it calls lowmem_page_address() which in turn calls
page_to_virt().  To prepare for this move, we move page_kasan_tag()
out of linux/mm.h into a separate lean header.

A side effect of this patch is that the <linux/kasan.h> include line
is moved inside the "#ifdef CONFIG_KASAN..." block, i.e. it is not
included at all if KASAN is disabled.

Signed-off-by: Max Kellermann <max.kellermann@xxxxxxxxx>
---
 MAINTAINERS                       |  1 +
 include/linux/mm.h                | 56 +-------------------------
 include/linux/mm/page_kasan_tag.h | 66 +++++++++++++++++++++++++++++++
 3 files changed, 68 insertions(+), 55 deletions(-)
 create mode 100644 include/linux/mm/page_kasan_tag.h

diff --git a/MAINTAINERS b/MAINTAINERS
index b43102ca365d..f2d32e2da433 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -14218,6 +14218,7 @@ F:	include/linux/mempolicy.h
 F:	include/linux/mempool.h
 F:	include/linux/memremap.h
 F:	include/linux/mm.h
+F:	include/linux/mm/*.h
 F:	include/linux/mm_*.h
 F:	include/linux/mmzone.h
 F:	include/linux/mmu_notifier.h
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0436b919f1c7..e140ee45f49c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2,6 +2,7 @@
 #ifndef _LINUX_MM_H
 #define _LINUX_MM_H
 
+#include <linux/mm/page_kasan_tag.h>
 #include <linux/errno.h>
 #include <linux/mmdebug.h>
 #include <linux/gfp.h>
@@ -27,7 +28,6 @@
 #include <linux/sizes.h>
 #include <linux/sched.h>
 #include <linux/pgtable.h>
-#include <linux/kasan.h>
 #include <linux/memremap.h>
 #include <linux/slab.h>
 
@@ -1818,60 +1818,6 @@ static inline void vma_set_access_pid_bit(struct vm_area_struct *vma)
 }
 #endif /* CONFIG_NUMA_BALANCING */
 
-#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
-
-/*
- * KASAN per-page tags are stored xor'ed with 0xff. This allows to avoid
- * setting tags for all pages to native kernel tag value 0xff, as the default
- * value 0x00 maps to 0xff.
- */
-
-static inline u8 page_kasan_tag(const struct page *page)
-{
-	u8 tag = KASAN_TAG_KERNEL;
-
-	if (kasan_enabled()) {
-		tag = (page->flags >> KASAN_TAG_PGSHIFT) & KASAN_TAG_MASK;
-		tag ^= 0xff;
-	}
-
-	return tag;
-}
-
-static inline void page_kasan_tag_set(struct page *page, u8 tag)
-{
-	unsigned long old_flags, flags;
-
-	if (!kasan_enabled())
-		return;
-
-	tag ^= 0xff;
-	old_flags = READ_ONCE(page->flags);
-	do {
-		flags = old_flags;
-		flags &= ~(KASAN_TAG_MASK << KASAN_TAG_PGSHIFT);
-		flags |= (tag & KASAN_TAG_MASK) << KASAN_TAG_PGSHIFT;
-	} while (unlikely(!try_cmpxchg(&page->flags, &old_flags, flags)));
-}
-
-static inline void page_kasan_tag_reset(struct page *page)
-{
-	if (kasan_enabled())
-		page_kasan_tag_set(page, KASAN_TAG_KERNEL);
-}
-
-#else /* CONFIG_KASAN_SW_TAGS || CONFIG_KASAN_HW_TAGS */
-
-static inline u8 page_kasan_tag(const struct page *page)
-{
-	return 0xff;
-}
-
-static inline void page_kasan_tag_set(struct page *page, u8 tag) { }
-static inline void page_kasan_tag_reset(struct page *page) { }
-
-#endif /* CONFIG_KASAN_SW_TAGS || CONFIG_KASAN_HW_TAGS */
-
 static inline struct zone *page_zone(const struct page *page)
 {
 	return &NODE_DATA(page_to_nid(page))->node_zones[page_zonenum(page)];
diff --git a/include/linux/mm/page_kasan_tag.h b/include/linux/mm/page_kasan_tag.h
new file mode 100644
index 000000000000..1210c62170a3
--- /dev/null
+++ b/include/linux/mm/page_kasan_tag.h
@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MM_PAGE_KASAN_TAG_H
+#define _LINUX_MM_PAGE_KASAN_TAG_H
+
+#include <linux/types.h>
+
+struct page;
+
+#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
+
+#include <linux/kasan.h>
+#include <linux/mm_types.h> // for struct page
+
+/*
+ * KASAN per-page tags are stored xor'ed with 0xff. This allows to avoid
+ * setting tags for all pages to native kernel tag value 0xff, as the default
+ * value 0x00 maps to 0xff.
+ */
+
+static inline u8 page_kasan_tag(const struct page *page)
+{
+	u8 tag = KASAN_TAG_KERNEL;
+
+	if (kasan_enabled()) {
+		tag = (page->flags >> KASAN_TAG_PGSHIFT) & KASAN_TAG_MASK;
+		tag ^= 0xff;
+	}
+
+	return tag;
+}
+
+static inline void page_kasan_tag_set(struct page *page, u8 tag)
+{
+	unsigned long old_flags, flags;
+
+	if (!kasan_enabled())
+		return;
+
+	tag ^= 0xff;
+	old_flags = READ_ONCE(page->flags);
+	do {
+		flags = old_flags;
+		flags &= ~(KASAN_TAG_MASK << KASAN_TAG_PGSHIFT);
+		flags |= (tag & KASAN_TAG_MASK) << KASAN_TAG_PGSHIFT;
+	} while (unlikely(!try_cmpxchg(&page->flags, &old_flags, flags)));
+}
+
+static inline void page_kasan_tag_reset(struct page *page)
+{
+	if (kasan_enabled())
+		page_kasan_tag_set(page, KASAN_TAG_KERNEL);
+}
+
+#else /* CONFIG_KASAN_SW_TAGS || CONFIG_KASAN_HW_TAGS */
+
+static inline u8 page_kasan_tag(const struct page *page)
+{
+	return 0xff;
+}
+
+static inline void page_kasan_tag_set(struct page *page, u8 tag) { }
+static inline void page_kasan_tag_reset(struct page *page) { }
+
+#endif /* CONFIG_KASAN_SW_TAGS || CONFIG_KASAN_HW_TAGS */
+
+#endif /* _LINUX_MM_PAGE_KASAN_TAG_H */
-- 
2.39.2